The tetradecapeptide somatostatin was characterized by Guillemin et al. and is described in U.S. Pat. No. 3,904,594 (Sept. 9, 1975). The tetradecapeptide has the formula: ##STR2## wherein there is a bridging bond between the sulfhydryl groups of the two cysteinyl amino acid residues. The tetradecapeptide in its linear form (sometimes referred to as dihydrosomatostatin), as well as analogs wherein this bridging bond is not present and is replaced by hydrogen, are for purposes of this application considered to be included in the definition "somatostatin analogs" as they appear to have substantially the same biological activity.
Somatostatin and many analogs of somatostatin exhibit activity in respect to the inhibition of growth hormone(GH) secretion from cultured, dispersed rat anterior pituitary cells in vitro and also in vivo, and with respect to the inhibition of insulin and glucagon secretion in vivo in the rat and in other mammals. Somatostatin has also been found to inhibit the secretion of gastrin and secretion by acting directly upon the secretory elements of the stomach and pancreas respectively. Its ability to inhibit the secretion of such hormones, allows somatostatin to be therapeutically employed in clinical conditions for the treatment of acromegaly, pancreatic islet cell tumors, diabetes mellitus and gastrointestinal bleeding. Because somatostatin has these properties, they must be taken into consideration whenever it is administered in vivo. The search has continued for somatostatin analogs which are potent in their effect in the gut but which are less potent than somatostatin in their inhibitory functions.